A display apparatus for displaying a stereoscopic video typically includes a display portion such as a liquid crystal panel or a PDP (plasma display panel) and a parallax barrier or a lenticular lens situated between the display portion and an observer. The display portion simultaneously displays a left image to be observed by the left eye and a right image to be observed by the right eye. The parallax barrier or lenticular lens separates image light emitted from the display portion to generate left image light, which corresponds to the left image and enters the left eye, and right image light, which corresponds to the right image and enters the right eye. Consequently, the observer may stereoscopically perceive a video displayed on the display portion without a dedicated eyewear device.
FIG. 51 is a schematic view of the aforementioned display apparatus 900 (c.f. “Autostereoscopic 3D Displays using Image-Splitter Method”, Journal of The Institute of Image Information and Television Engineers, Vol. 51, No. 7, pp. 1070-1078, (1997)). The display apparatus 900 is described with reference to FIG. 51.
The display apparatus 900 includes a display panel 910 and a parallax barrier 920. The display panel 910 displays vertical strips (denoted by the symbol “L” in FIG. 51) representing a left image and other vertical strips (denoted by the symbol “R” in FIG. 51) representing a right image. The vertical strips of the left and right images are alternately arranged in the horizontal direction. The parallax barrier 920 includes barrier strips 921 which shield image light emitted from the display panel 910. The barrier strips 921 extend in the vertical direction, like the vertical strips. Openings 922 to allow transmission of the image light are formed between the barrier strips 921.
The left and right images represent contents which are different from each other by binocular parallax. Due to the binocular parallax set between the left and right images, the observer may composite a stereoscopic image from the left and right images.
When the observer faces the display apparatus 900 from an appropriate position, image light emitted from the vertical strips of the left image reaches the left eye of the observer whereas image light emitted from the vertical strips of the right image reaches the right eye of the observer. Meanwhile, the barrier strips 921 shield image light, which propagates towards the right eye of the observer from the vertical strips of the left image, and also shield image light which travels towards the left eye of the observer from the vertical strips of the right image. Consequently, the observer may appropriately observe a stereoscopic image displayed on the display apparatus 900.
The display apparatus 900 shown in FIG. 51 faces problems about interference fringes (moiré). Moiré is dependent on a relationship between a pattern of the openings 922 in the parallax barrier 920 and an arrangement pattern of pixels of the display apparatus 900. It is known that moiré conditions depend on a width and a shape of the openings 922 in the parallax barrier 920.
The display panel 910 includes a display surface on which images (the left and right images) are displayed. The display surface is formed by pixels arranged in a matrix pattern. The pixels typically include R sub-pixels which emit red light, G sub-pixels which emit green light, and B sub-pixels which emit blue light. If the display panel 910 is a liquid crystal panel or a PDP, the display surface includes a black matrix which is arranged along boundaries among the R, G and B sub-pixels to prevent mixture among the red, green and blue lights. It should be noted that in the case of a liquid crystal panel, the black matrix may be referred to as a rib.
The display panel 910 may include supporting electrodes which are superimposed on the aforementioned sub-pixels. The aforementioned black matrix and the supporting electrode cause dark regions on the sub-pixels. Therefore, through the openings 922, the observer may perceive relatively dark regions created at positions corresponding to the black matrix or the supporting electrodes and relatively bright regions without the black matrix and the supporting electrode. At specific observing positions from the display apparatus 900, the observer may recognize openings 922 where many bright regions are exposed as well as openings 922 where many dark regions are exposed. Consequently, the observer perceives an uneven luminance pattern (moiré) on the display surface. This means significantly degraded image quality.
FIG. 52A is a photograph showing a stepped barrier 923, which is exemplified as a parallax barrier, and a moiré pattern caused under usage of the stepped barrier 923. FIG. 52B is a photograph showing a slanted barrier 924, which is exemplified as a parallax barrier, and a moiré pattern caused under usage of the slanted barrier 924. A parallax barrier and a moiré pattern are described with reference to FIGS. 52A and 52B.
The stepped barrier 923 shown in FIG. 52A includes barrier portions 925 each of which has a stepped contour. Rectangular openings 926 arranged in a stepped manner are formed between the barrier portions 925. A display panel (not shown) is situated behind the stepped barrier 923. The display panel displays an overall white image over the entire display surface. The barrier portions 925 block emitted image light from the display surface whereas the image light is transmitted through the openings 926. It should be noted that a width (horizontal dimension) of the opening 926 is approximately equal to a width of each of the sub-pixels which form the display surface (opening ratio: 1).
A mixture ratio between a sub-pixel region and a black matrix region, which are observed through the openings 926, depends on an observing position of an observer. Accordingly, a moiré pattern in a grid is caused as shown in FIG. 52A.
A slanted barrier 924 shown in FIG. 52B includes barrier portions 927 each of which has a contour inclined from the vertical line. Continuous openings 928 inclined from the vertical line are formed between the barrier portions 927. A display panel (not shown) is situated behind the slanted barrier 924. The display panel displays an overall white image over the entire display surface. The barrier portions 925 block emitted image light from the display surface whereas the image light transmits through the openings 928. It should be noted that a width (horizontal dimension) of the opening 928 is approximately equal to a width of each of the sub-pixels which form the display surface (opening ratio: 1).
In comparison to the aforementioned stepped barrier 923, there is a small variation in the area of observed sub-pixels through the opening 928 of the slanted barrier 924 under variation of observing position of the observer. Therefore, the stepped barrier 923 causes moiré with less contrast than the stepped barrier 923 does. In particular, the observer is less likely to observe a moiré pattern extending in the horizontal direction. However, the slanted barrier 924 still causes a moiré pattern which is perceivable for the observer.
As described above, both of the stepped and slanted barriers 923, 924 cause moiré patterns which are visible to the observer. The moiré pattern becomes more noticeable when the display panel displays a two-dimensional image than when the display panel displays a stereoscopic image.
FIG. 53 is a schematic view of a barrier pattern proposed by Patent Document 1 (US Patent Application Publication No. 2005/0073472). Techniques disclosed in Patent Document 1 are described with reference to FIG. 53.
The techniques according to Patent Document 1 utilize a first plate 931, which has an opening pattern at first intervals, and a second plate 932, which has an opening pattern at second intervals. The second plate 932 is tilted at a predetermined angle with respect to the first plate 931 and overlaid on the first plate 931. According to Patent Document 1, moiré is reduced when the barrier pattern is tilted within a range of 20 to 30 degrees with respect to pixels.
The inclination of the barrier pattern with respect to the pixels reduces a resultant variation in an observed area of the pixels from a positional change of observation, which results in less noticeable moiré. However, unnecessary pixels are more likely to be exposed through the barrier pattern as the barrier pattern tilts. Therefore, crosstalk (a phenomenon in which a ghost image, a blurry image, or an unnatural image is observed because of a left image being observed by both of the left and right eyes) is more likely to happen.
FIG. 54 is a schematic view of a parallax barrier 940 disclosed in Patent Document 2 (U.S. Pat. No. 7,268,943). The conventional parallax barrier 940 is described with reference to FIG. 54.
Openings 941 extending in the vertical direction are formed in the parallax barrier 940. In FIG. 54, an interval between the openings 941 is denoted by the symbol “S”. The parallax barrier 940 includes zigzag contour portions 942 which define a shape of the opening 941. The contour portions 942 form protrusions 943 which protrude toward the center line of the opening 941. The protrusions 943 are periodically arranged in the vertical direction to form a tooth profile.
The openings 941 with the tooth profile sufficiently mix a region of pixels exposed through the openings 941 (a relatively bright region) with a region of a black matrix exposed through the openings 941 (a relatively dark region), which results in decreased moiré. On the other hand, since the openings 941 have a large area, crosstalk becomes noticeable. Therefore, an observer is likely to observe blurry images. In addition, because of the large area of the openings 941, the tooth profile defined by the contour portion 942 may deteriorate image quality although it depends on a number of viewpoints defined by the parallax barrier 940.
FIG. 55 is a schematic view of a parallax barrier with various openings disclosed in Patent Document 3 (WO 2010/007787). The parallax barrier according to Patent Document 3 is described with reference to FIG. 55.
The parallax barrier according to Patent Document 3 defines several viewpoints. The parallax barrier according to Patent Document 3 has various openings shaped by a zigzag pattern or a curved pattern. Since the openings are shaped by elliptical arc curves, left and right images, which are adjacent to each other, become mixed. Accordingly, for example, if the parallax barrier defines first to fourth viewpoints, a feeling of strangeness felt by an observer is reduced at a jump point where the first viewpoint is switched to the fourth viewpoint. However, since the mixture of the left and right images means crosstalk growth, the observer may observe significantly blurry images.
The aforementioned various techniques reduce moiré contrast but increase crosstalk. In short, there is a tradeoff between moiré contrast and crosstalk.